Apparatus for sharpening cutting edges electrolytically



APPARATUS FOR SHARPENING CUTTING EDGES ELECTROLYTICALLY Filed Jan. 24.1966 NVENTORI" 0WBw- I 2m gal ATTQQNEYJ.

United States Patent 01 ice 3,551,316 APPARATUS FOR SHARPENING CUTTINGEDGES ELECTROLYTICALLY Robert J. Gale, Swindon, Wiltshire, England,assignor t Wilkinson Sword Limited, London, England, a British companyFiled Jan. 24, 1966, Ser. No. 522,668 Claims priority, application GreatBritain, Jan. 28, 1965, 3,736/ 65 Int. Cl. B01k 3/00 US. Cl. 204-206 8Claims ABSTRACT OF THE DISCLOSURE An electrolytic cell forelectroforming or electrofinishing the cutting edge of a razor bladecomprises screening means adjacent which the edge of the razor blade islocated, so that the passage of electric current from the razor blade tothe cathode of the cell is limited in a differential manner. As aconsequence more metal is removed from the tip of the blade andprogressively less metal as the distance from the tip increases.

This invention relates to the production of cutting edges and, moreparticularly, to the production of the cutting edges of razor blades.

The invention employs electrolytic processing in the production of thecutting edges. The electrolytic processes may be used for the finishing,only, of cutting edges after initial formation by other methods, such asabrasive methods, and such processing will be referred to hereafter aselectrofinishing. On the other hand, the processing may be used forproduction of a cutting edge, without prior mechanical shaping, in whichcase such processing will be referred to hereafter as electroforming.

According to the present invention there is provided the method ofelectroforming of electrofinishing a cutting edge of a razor blade by anelectrolytic process, wherein the volume of electrolyte in the region ofthe blade where the cutting edge is to be produced is restricted,whereby a cutting edge having facets of desired surface contour isformed.

The invention also provides the method of electroforming orelectrofinishing the cutting edge of a razor blade in which the razorblade blank is made anodic in an electrolytic cell, wherein the flow ofcurrent from the neighbourhood of the blade edge is limiteddifferentially in such a manner that more metal is removed from the tipof the blade than from areas further from the tip.

There is further provided by the invention an electrolytic cell forelectroforming or electrofinishing the cutting edge of a razor bladecomprising means for limiting the passage of current from the razorblade to the cathode in a differential manner whereby more metal isremoved from the tip and progressively less metal as the distance fromthe tip increases.

One method of performing the invention, an apparatus therefor will nowbe described by way of example, with reference to the accompanyingdrawings, in which:

FIG. 1 is a side elevation of an electrolytic cell forpartial-electroforming or electrofinishing of the cutting edge of arazor blade,

FIG. 2 is an underside plan view of the cell of FIG. 1, and

FIG. 3 is a perspective sectional view through the cell at line III-IIIin FIG. 1.

The basic cell construction is a modification of the cell described inUS. patent application Ser. No. 450,718 of B. W. Lovekin filed Apr. 26,1965 and assigned to the same assignee as is the present application.

3,551,316 Patented Dec. 29, 1970 The associated apparatus with which thecell is used for the electroforming or electrofinishing of the cuttingedges of razor blades may be as described in the specification of theabove-mentioned patent application, more particularly in connection withFIG. 1 of the drawings accompanying that patent application.

Referring now to the accompanying drawings, it will be seen that thecell comprises a metal housing 10 which constitutes the cathode of thecell and which is maintained at earth potential by making an earthconnection to earth terminal 11. Within the cathode housing 10 twoscreening masks 12, 12 (FIG. 3) of ceramic material are mounted and theadjacent faces of these are separated by a sufficient distance to allowthe passage of the metal strip 13, in the form of razor blade blanksjoined end-toend'with central slot already punched. The strip 13 makes asliding fit with the faces of masks 12, 12, the separating of the masks12, 12 being adjustable by means of adjusting screws 21. The masks 12,12 each have a central aperture in which an elongated anode 14 ismounted to form an electrolyte containing anode chamber 12a, 12a betweenthe blade strip 13 and the respective anode 14, 14. External connectionto the anodes is made through four terminals 15 which extend through thewall of the cathode housing 10, being insulated therefrom by insulators16. The masks 12, 12 are also shaped to provide cathode chambers 12b,1211 whose shape will be described in greater detail hereafter. Fourinlet ports 17 for electrolyte are provided towards one end of the cell,two to feed electrolyte under pressure through the two anode chambers12a, 12a and the other two to feed electrolyte through the two cathodechambers 12b, 12b. Four corresponding outlet ports 18 are providedtowards the other end of the cell. The final portion of the cell at eachend beyond the ports 17, 18 is closed by a manifold of insulatingmaterial such as ceramic or plastic, for examplepolytetrafiuoroethylene. Air is fed under pressure to each manifoldthrough a respective air inlet port 19 and through labyrinth seals (notshown) in the manifold to a respective outlet port 20 in order to forman air seal to prevent, or substantially reduce, escape of electrolyte.

The current path is from each anode 14 through the electrolyte in itsrespective anode chamber 12a to the central portion of the blade strip13, through the blade strip to the exposed surface at each edge andthence through the electrolyte in the respective cathode chamber 12b tothe cathode. The novel electrode arrangement is the subject of aco-pending patent application.

With the present invention there is a restriction on the amount ofelectrolyte in the region at each edge of the blade where the facets ofthe cutting edge are to be formed, this restriction of the electrolytefacilitating the production of facets of desired surface contour forreasons which will be discussed in greater detail below. One method ofachieving this, which is shown in FIG. 3, is by shaping the screeningmasks 12 so that each cathode chamber is formed with a channel intowhich projects the edge of the blade strip 13 at which the facets of thecutting edge are to be produced. As illustrated the channels areV-shaped in cross-section but many other shapes may be employed. Forexample, the channel may be parallel-sided or may be flared with otherthan a V-shaped cross-section. The angle of inclination of the sides ofthe channel will be chosen in dependence upon the operating conditions,such as current density and electrolyte, but by way of example, whereelectroforming is to be per formed the cell, or at least the initialsection thereof, could typically have an included angle for the channelof that is to say the surface of each mask being inclined at 40 to themajor plane of the blade strip. For electrofinishing of an alreadypartially formed edge the included angle may, for example, by 60 or evenas little as 40. The amount of the edge of the blade strip whichprojects into the channel is a matter of choice dependent upon thedesired extent and form of the facets of the finished razor blade, butfor typical double-edged razor blades the amount might be between 0.6and 1.3 mm. The principal effect of the amount of electrolyte decreasingprogressively from the mouth of the channel inwards is that the currentflowing to the strip is increasingly limited away from the tip of thestrip. The consequence is that because the current is greatest at thetip of the blade and decreases with increasing distance from the tip,there is greater removal of metal from the tip and progressivelydecreasing removal of metal with increasing distance from the tip. Inthis way choice of an appropriate crosssection for the channel permitsthe formation of facets of desired shape appropriate for razor blades.For example, in contrast to the planar facets normal when forming arazor blade cutting edge by abrasive methods the facets may have aconvex contour.

It will be understood that the strip may be fed in succession through anumber of cells having screening masks providing channels of differentcross-section, with the channels in successive cells being progressivelynarrower as the facets approach more nearly to their final form.Alternatively the contour of the masks in a single cell may changeeither progressively or in steps with the same object. In the case ofelectrofinishing, the masking conditions will be less critical the morenearly the edge has been formed to its final shape prior to theelectrolytic treatment.

Whilst reference has been made to the use of ceramic material for themasks, other insulating materials may be used such as plastics, inparticular polytetrafluoroethylene. On the other hand metal may be usedfor the masks by insulating the masks from the cathode and using themasks as anodes. In this event the metal employed should be such that itis polarised in the operational condition of the cell so that the maskscan provide a conductive connection to that portion of the strip withwhich they are in physical contact but so that there is negligibleconducion between the electrolyte and the exposed surfaces of the masks.Examples of suitable metals of which such masks may be composed aretitanium, tungsten, tantalum, niobium or zirconium. Completepolarisation of the material is not essential because effectivedissolution of the strip would still be possible even if the maskscarried a low proportion of the current.

Although reference has been made to the unidirectional potentialsalternating current may be used for the processing.

Masks can also be used where razor blade blanks are processed in stacksby interleaving blade blanks with masks. However, another method ofprocessing blanks in stacks is partly to form a cutting edge on theblanks by mechanical methods, such as by abrasive removal of metal or bypressing, to provide facets such that when the blade blanks aresuperposed one on the other only the facets are exposed and the channelsbetween each pair of adjacent facets acts to limit the currentdifferentially in the manner described above.

A preferred electrolyte, which is the subject of a copending patentapplication, has the composition 35 to by weight of phosphoric acid, 5to 15% by weight of sulfuric acid, 0 to 8% chromium trioxide and thebalance water, the bath operating temperature being for example between55 and C.

The invention is not restricted to the formation of cutting edges onrazor blades but is applicable to the formation of other types ofcutting edges.

I claim:

1. In an electrolytic cell for at least finishing the cutting edge of arazor blade,

an elongated cathode,

means for electrically connecting said cathode to a negative terminal ofa source of current,

at least one anode, and

means for connecting said anode to the positive terminal of said sourceof current, and

guide means for supporting a razor blade having at least one unfinishedcutting edge in predetermined position relative to said cathode and saidanode, said guide means and said cathode defining a first elongatedspace for containing electrolyte in contact with said cathode, saidunfinished cutting edge projecting into said electrolyte,

the combination with said guide means of surfaces thereon which in thevicinity of the edge of the razor blade are inclined at between 20degrees and 40 degrees to the major plane of the blade and said surfacesbeing substantially planar to form an electrolyte passage which in thevicinity of the blade is of diverging cross-section.

2. A cell according to claim 1 wherein said surfaces are inclined atapproximately 30 to the major plane of the blade.

3. A cell according to claim 1 wherein said surfaces abut the blade at adistance of between about 0.025 and 0.050 inch from the tip of thecutting edge.

4. A cell according to claim 1 wherein said surfaces abut the blade at adistance of approximately 0.030 inch from the tip of the cutting edge.

5. A cell according to claim 1 wherein said guide means is of a ceramicmaterial.

6. A cell according to claim 1 wherein said guide means is of a plasticsmaterial.

7. A cell according to claim 1 wherein said guide means is of a metalwhich is at least partially polarised in the operational condition ofthe cell.

8. A cell according to claim 1 wherein the blade is part of an elongatedstrip from which a number of blades are produced and the blade is movedthrough the cell during processing, the divergence in cross-section inthe direction of the tip becoming less as the blade progresses throughthe cell.

References Cited UNITED STATES PATENTS 2,974,097 3/1961 Ramirez et al204-206 3,399,130 8/1968 Lovekin 204-206 ROBERT K MIHALEK, PrimaryExaminer U.S. Cl. X.R.

